The present invention relates to a cemented carbide end mill with three or more cutting edges that can perform drilling, grooving and side-surface cutting with high efficiency in milling operations.
The cemented carbide end mill comprises peripheral cutting edges and end cutting edges. A conventional three-flute cemented carbide end mill, when viewed in across section perpendicular to an axis of the end mill as shown in FIG. 3b, has a ratio of about 1 to 6 between a land width L1 of a flank 14 of a peripheral cutting edge 3 and a width L2 of a flute 15. According to the definition given by The Japanese Industrial Standard (JIS), xe2x80x9cland widthxe2x80x9d is defined as xe2x80x9cthe width of landxe2x80x9d and xe2x80x9clandxe2x80x9d is defined as xe2x80x9cThe part having bank state width from cutting edge to heel of milling cutter having slots (flutes). Further, xe2x80x9cflutexe2x80x9d is defined as xe2x80x9cThe dent part between the neighboring cutting edge and the heel. Therefore, xe2x80x9cthe land width L1xe2x80x9d is the width from a cutting edge 3 to heel 19, and this width is measured as shown in the FIG. 3b, the radial width between a line passing both a cutting edge 3 and an axis 0 of the end mill, and a parallel line thereto passing through heel 19. And xe2x80x9cthe flute width L2xe2x80x9d is drawn as the distance between the neighboring cutting edge 3 and heel 19 from the definition of the xe2x80x9cflutexe2x80x9d. A core diameter d1 is about 60%-70% of an outer diameter 17. The flute 15 has a 60%-70% slant portion 15a in a shape bulging radially outwardly. FIGS. 3a and 3c illustrates a conventional two-flute end mill and four-flute end mill, respectively.
JP-2000-52127A discloses an end mill of a different shape. This end mill, when viewed in a cross section perpendicular to the peripheral cutting edges, has its flute surfaces assuming a continuous concave shape, its core diameter of about 60%-75% of the outer diameter and its helix angle of about 30xc2x0-50xc2x0.
In conventional cemented carbide end mills, a two-flute end mill is mainly used for hole drilling and groove cutting. In side surface machining, three- and four-flute end mills are more advantageous than the two-flute end mills in terms of machining efficiency and precision. In hole drilling and groove cutting, on the other hand, the three- and four-flute end mills are not good at chip discharging capability, and have a problem that cut grooves are inclined or their corners are severely worn out.
An object of the present invention is to solve the above-described problem of the conventional art and provide a cemented carbide end mill with three or more cutting edges, which has a good chip discharging capability even in the hole drilling and groove cutting and which minimizes the tilting of cut grooves and the corner wear of the end mill.
The invention solves the above-described problem by the cemented carbide-coated end mill constructed as follows. The cemented carbide end mill has three or more cutting edges formed on its periphery and a plurality of flutes each provided between adjacent cutting edges. Each of the cutting edges has a base material of ultra-fine cemented carbide allow containing 10%-14% cobalt and is coated with a titanium-aluminum nitride hard film. Each flute has a helix angle of 35xc2x0-60xc2x0 and, when viewed in a cross section perpendicular to the end mill axis, is in a shape generally concave radially inwardly. The cutting edges and the flutes are so formed that the ratio of the land width to the flute width is 1:1.5 to 1:4, and that the core diameter is 62%-68% of the diameter of the end mill, wherein the land width is the width from the cutting edge to heel, and the flute width is the distance between the neighboring cutting edge and heel.
With this construction, the cutting edges are greatly improved in tenacity because of the base material of ultra-fine cemented carbide alloy containing 10%-14% cobalt, and are improved in wear resistance because of the titanium-aluminum nitride hard film coated thereon. In addition, the ratio of the land width to the flute width, when viewed in a cross section perpendicular to the axis of the cutting edges, is set at 1:1.5 to 1:4 so as to increase the land width. This increases the rigidity of the end mill and thus can reduce the inclination of cut grooves and the corner wear of the end mill. The flutes, because of the generally concave bottom shape, facilitate the curling of chips and forcibly discharge them. Further, setting the flute helix angle at 35xc2x0-60xc2x0 intends to both reduce the cutting resistance and increase the end mill strength against fracture.
Between the heel and a flute bottom, the flute may comprise two generally concave portions and be in a shape in which these two portions are intersected such that the intersecting point protrudes radially outwardly.
Each of the cutting edges preferably has a first flank following the cutting edge and a second flank connecting the first flank and the flute, and the second flank is in a shape generally concave radially inwardly. With this structure, a stepped portion in a conventional end mill that follows the flank of a cutting edge is replaced with the smooth curved surface to enable further enhancement of the rigidity of the end mill.
In the case of a three-flute end mill, it is preferable that the land width-to-flute width ratio is 1:2 to 1:4 and the flute helix angle is 40xc2x0-60xc2x0.
In the case of a four-flute end mill, it is preferable that the land width-to-flute width ratio is 1:1.5 to 1:3 and the flute helix angle is 35xc2x0-45xc2x0.